1. Field of the Invention
The present invention generally relates to a disk drive of a magnetic recording method, and in particular, a disk drive device provided with a function of avoiding malfunctions by a magnetic field of magnetic disturbance.
2. Description of the Related Art
In recent years, in the field of a disk drive of a magnetic recording method, a perpendicular magnetic recording method has been noted along with the development of a longitudinal magnetic recording method. In this perpendicular magnetic recording method, a practical use of the a disk drive using a double-layered disk is promoted as a magnetic recording medium in this perpendicular magnetic recording method.
The double-layered structure disk has a recording layer showing magnetic anisotropy in a perpendicular direction, a soft magnetic layer between the recording layer and a substrate. The soft magnetic layer has a so-called function of allowing a part of magnetic flux generated from a magnetic pole on one side of a head to pass therethrough to the other magnetic pole to support a recording operation of the head. The soft magnetic layer has a characteristic of being magnetized and returning to an original non-magnetized state, and is provided with a characteristic of a high sensitivity against an outside magnetic field.
From such characteristic, the soft magnetic layer is likely to be affected by the magnetic influence with the magnetic field of the magnetic disturbance in the case where magnetic disturbance is generated with respect to the disk drive. The possibility becomes high that the magnetic state of the recording layer of the disk unstably changes along with the magnetic change of this soft magnetic layer. In particular, when the magnetic disturbance with a strong magnetic field is generated at the time of the read/write operation, there is a high possibility that the record data written with a write head which is a magnetic head or the read data which is read with the read head changes. In the worst case, malfunctions of the read/write operation are invited, and erroneous data is recorded or read.
As described above, in particular, in a disk drive of the perpendicular magnetic recording method using the double-layered structure disk, a counter-measure for avoiding malfunctions of the read/write operation of the data by the magnetic field of the magnetic disturbance becomes indispensable.
Conventionally, there is proposed a technique in which a magnetic thin film for magnetic shield is provided on the protection film of the head is provided, and the influence of the magnetic disturbance to the disk is prevented (for example, see Jpn. Pat. Appln. KOKAI Publication No. 4-137209).
Furthermore, as a different proposal, there is available a method of reducing a magnetic permeability of the soft magnetic layer of the disk (for example, see Jpn. Pat. Appln. KOKAI Publication No. 2000-90424).
Furthermore, there is proposed a method of detecting a magnetic field of the magnetic disturbance and generating a magnetic field for correction for eliminating the magnetic field (for example, see Jpn. Pat. Appln. KOKAI Publication No. 3-44809).